In the field of electronics such as liquid crystal display devices as well as semiconductor such as LSI, it is important to form a thin film with a high degree of accuracy, and therefore it is required to measure thickness of a thin film with a high degree of accuracy.
Patent Document 1, for example, proposes a film thickness measurement device capable of measuring a thickness of a transparent or translucent thin film formed on a substrate by illuminating measurement light to a transparent glass substrate for producing a liquid crystal display device, and by alternately transmitting the measurement light and receiving reflected light of the measurement light from the substrate between a measuring unit main body and a sensor unit via an optical fiber, as well as a film thickness measurement method.